# Eccentricity-dependent saccadic reaction time: The roles of foveal magnification and attentional orienting

## TL;DR

The study shows that adjusting target size based on foveal magnification can reduce saccadic reaction time increases caused by target distance from the fovea.

## Contribution

The novel finding is that scaling targets according to foveal magnification eliminates eccentricity-dependent saccadic reaction time increases.

## Key findings

- Saccadic reaction times increase with target eccentricity for equal-sized targets.
- Scaling targets according to foveal magnification eliminates this increase, especially for low-contrast targets.
- The increase in reaction time persists in delayed saccades, independent of target scaling.

## Abstract

The primate visual brain is characterized by foveal magnification. Here, we show in macaque monkeys that foveal magnification affects the dynamics of saccade initiation. In a visually guided saccade task, saccadic reaction times (SRT) increased with target eccentricity. Notably, we effectively eliminated this increase by scaling the target size according to the foveal magnification factor in the superior colliculus. We then repeated the comparison between non-scaled and scaled targets while changing the task to a delayed, visually guided saccade task. In this task, the saccade was triggered by the foveal fixation offset rather than target onset, such that target onset long before the fixation offset was essentially irrelevant for SRT. In this task, we found that SRT increased with target eccentricity, with a similar rate for both non-scaled and scaled targets, consistent with an attentional scan from the fovea to the target, a recently hypothesized general mechanism of attention.

•For equal-sized targets, saccadic reaction times increase with target eccentricity•This increase is eliminated by scaling targets according to foveal magnification•Scaling is most effective for low-contrast targets•The increase persists in delayed saccades, independent of scaling

For equal-sized targets, saccadic reaction times increase with target eccentricity

This increase is eliminated by scaling targets according to foveal magnification

Scaling is most effective for low-contrast targets

The increase persists in delayed saccades, independent of scaling

Neuroscience